Uncovering secrets in the ‘Aldabra of the Amirantes’

Worldwide, our oceans are in trouble and island nations like the Seychelles are especially vulnerable to changes to marine ecosystems. International organisations have called on countries to safeguard their marine resources by creating an effective network of marine reserves that protect important habitats and make fish stocks more sustainable in the long term. St Joseph Atoll, a critical nursery site in the Outer Islands, would play a valuable role in the Seychelles’ network of marine protected areas.

Celebrated and protected for its natural splendour and heritage value, Aldabra Atoll is the pride of the Seychelles. Although few places in the world compare to Aldabra, the Seychelles shelters another gem in its Outer Islands: St Joseph Atoll. Being surrounded by a distinct, uninterrupted reef flat at low tide sets St Joseph apart from all other atolls in the Seychelles, giving it significance as a nursery, breeding and feeding area for multiple species. Although small, St Joseph is as important to the Seychelles as Aldabra is.

Together with neighbouring D’Arros Island, St Joseph Atoll provides an outstanding ocean observatory for scientific research and discovery. From its base on D’Arros, the Save Our Seas Foundation D’Arros Research Centre (SOSF-DRC) has demonstrated its commitment to research and discovery in the area. Showcasing the national and international significance of the island, the atoll and the surrounding waters, the SOSF-DRC aims to conserve the integrity of the natural environment for the Seychellois people today and in the future.

For more than a decade, the research centre on D’Arros has conducted baseline monitoring of the marine environment and, after combining with the Save Our Seas Foundation in 2012, it initiated additional new and innovative research projects. Coupled with long-term monitoring, these new projects help not only to provide a reference for the entire Amirantes Group, but also to answer crucial questions about the life histories of important marine species.

The SOSF-DRC supports 15 research projects, which include studies of 17 mega- fauna species such as the Vulnerable manta ray Manta alfredi, the Critically Endangered hawksbill turtle Eretmochelys imbricata and the Endangered green turtle Chelonia mydas. Broader ecosystem concerns relating to biodiversity and habitat rehabilitation are also among the research topics. Along with Danah Divers, the SOSF-DRC maintains the largest acoustic receiver network in the Western Indian Ocean, which consists of 88 receivers that track marine life over the entire Amirantes Bank. Over and above its commitment to research at St Joseph and D’Arros, the SOSF has supported an additional seven projects elsewhere in the Seychelles.

While the comprehensive research projects based at the SOSF-DRC focus on important conservation issues relating to both ecosystems and species, they also have future generations of the Seychellois people in mind.

Of course, the marine realm includes more than just what lies under the waves. What happens within the reefs, flats and lagoon of D’Arros and St Joseph are inextricably linked to what occurs above sea level on each tiny coralline island and sand cay in the group. The SOSF-DRC understands that to undertake the best research, a holistic approach to tropical island ecosystems must incorporate studies above the sea as well as below it.

While the heavy rain of coconuts from unmanaged former plantations continues to fall on D’Arros and the largest islands within St Joseph Atoll, forest rehabilitation efforts have expanded relic stands of indigenous broadleaf trees. Thus a new rain of nutrient-rich guano from returning seabirds enhances efforts to restore parts of the islands to their former ecological state. Because all islands in the group have been rat-free for more than a decade, these rehabilitated indigenous forests provide potential areas for the introduction of endangered endemic land birds – and a possible stronghold for Seychelles bird species under threat. Indeed, forest rehabilitation is likely to increase biodiversity within the whole system.

In 2017, the SOSF-DRC plans to initiate a terrestrial biodiversity assessment of the area by partnering with the University of Seychelles. This project aims to contribute to the broader national biodiversity database, such as the National Environmental Data and Information portal, as outlined in the most recent Seychelles National Biodiversity Strategy Action Plan. The opportunity for the SOSF-DRC to work closely with the University of Seychelles promotes capacity building for the Seychellois people and adds to the vision of a knowledge-based society.

Birds, including 15 breeding species, make up a large part of the biodiversity of St Joseph and D’Arros. Accordingly, the SOSF-DRC currently supports a research project on the most abundant seabird found in the area, the wedge-tailed shearwater Ardenna pacifica. Soaring in after foraging at sea for days at a time, the shearwaters, or fouquet in Seychellois Creole, gather in their tens of thousands as night falls on St Joseph and D’Arros. The colony is estimated to be the third largest in the Western Indian Ocean and the sheer numbers of these nesting seabirds provide an opportunity to uncover significant feeding areas for the species. As shearwaters frequently associate with tuna, studying this popu-lation may help the government of the Seychelles, a major tuna-fishing nation in the Western Indian Ocean, to better understand and manage its tuna stocks.

Photo by Thomas Peschak

Manta rays can have wingspans of more than six metres, yet they are filter feeders that eat only small planktonic organisms. Almost 100 reef mantas utilise the area around D’Arros and St Joseph as a feeding ground all year round, representing the largest and densest manta ray aggregation known in the Seychelles. Photo by Thomas Peschak

Between the shores and in the shallows

Similarly to above sea level, much happens between the land and the reef crest around St Joseph Atoll and D’Arros Island. While hawksbill and green turtles trust the undisturbed beaches to safeguard their precious nests, shallow sand flats provide crucial habitat and nursery grounds for various fish species, sharks and rays. The beaches and shallow waters of St Joseph and D’Arros have largely been protected from the resource harvesting, increasing human activity and excessive coastal development seen on many other islands in the Indian Ocean. Consequently, there exists an exceptional opportunity to study the animals and processes within this zone.

As a link between the ocean and islands, turtles rely on both healthy marine habitats and undeveloped beaches. Seychelles resident Dr Jeanne Mortimer heads the nesting turtle monitoring programme that is carried out predominantly by members of the Seychellois community living on D’Arros. Notably the longest-running programme of its kind in the Amirantes, this initiative has involved no fewer than 17 Seychellois individuals over the years. The direct decline in poaching observed as a result of their efforts speaks to the success of the programme. By taking ownership of the turtles and responsibility for their well-being, the monitors have ensured that more turtles are able to reproduce and carry on the species.

The additional long-term monitoring of juvenile turtles that forage in the safety of the waters around St Joseph and D’Arros has led to the recognition that these shallow waters are important for hawksbill and green turtles both locally and internationally. Since the 1970s, the local population of turtles has increased, presumably due to the undisturbed and undeveloped beaches. The SOSF-DRC’s commitment to turtle research has contributed to a better understanding of the nesting behaviour and population sizes of the turtles, as well as the growth rates and movements of the juveniles. The significant impact that these long-term research projects have had on the well-being of turtles in the Seychelles stretches well beyond the small area around St Joseph and D’Arros.

As much as the beaches are an important nesting area for turtles, the shallow waters of St Joseph Atoll provide shelter for newborn blacktip reef Carcharhinus melanopterus and sicklefin lemon Negaprion acutidens sharks. Accordingly, since 2014 the SOSF-DRC has supported the largest neonatal shark study in the Seychelles, which examines the habitats of the two species and the role of competition between them. Early results highlight the importance of St Joseph Atoll as a healthy nursery ground that, if protected, could help protect entire species from increasing threats. The study provides a better understanding of how sharks operate in a remote coastal ecosystem, which is applicable in the broader Seychelles as well as in local waters. Furthermore, understanding these complexities could help to provide a template for the management of communal shark nurseries in the Indian Ocean.

Although St Joseph Atoll teems with rays of three species – cowtail ray Pastinachus sephen, mangrove whiptail Himantura granulata and porcupine ray Urogymnus asperrimus – and is the feeding, breeding and nursery area for all three, very little scientific attention has been given to this role. The porcupine ray in particular is classified as Vulnerable on the IUCN Red List and although it is considered rare over much of its range, it is found in abundance in the atoll. Since 2014 an SOSF-DRC project has been studying the ecology of stingrays in St Joseph Atoll and aims to discover how these species link between apex and lower trophic levels within the atoll system. Studying and protecting them within the isolated system of St Joseph Atoll is vitally important for the conservation and management of each of these three species throughout their distributions.

Manta rays can have wingspans of more than six metres, yet they are filter feeders that eat only small planktonic organisms. Almost 100 reef mantas utilise the area around D’Arros and St Joseph as a feeding ground all year round, representing the largest and densest manta ray aggregation known in the Seychelles. Photo by Thomas Peschak

Manta rays bask in the channel between D'Arros and St Joseph. These waters are home to a large population of resident individuals. The DRC is investigating the ecology and movement of the rays using acoustic transmitters. Photo by Thomas Peschak

Beneath the waves

Under the sea exists a kaleidoscope of colour, a treasure trove of life. But because overexploitation, pollution and damage aren’t as visible beneath the waves as they are on land and beaches, extra precautions and special reserves are required to safeguard marine ecosystems. From the study of oceanographic systems to coral reef monitoring and manta ray ecology, the dedication of the SOSF-DRC to marine research is unmistakable.

Understanding oceanographic trends is the backbone for recognising broad drivers of animal movements and ecology. For this reason, the SOSF-DRC monitors relevant ambient environmental data such as tidal movements, light intensity and temperature. Every five minutes since 2011, no fewer than 100 temperature loggers have recorded the sea temperature in the waters surrounding the island and atoll. Early analysis of data from loggers at five metres highlights a significant annual temperature change of nearly 7 °C, which probably affects animal movements and foraging around both St Joseph and D’Arros. These results may ultimately help to predict the severity of bleaching events and estimate the mortality or recovery of corals after the events.

By monitoring the marine environment around St Joseph and D’Arros, researchers are able to detect changes in good time. The earlier they perceive these changes, the sooner they can try to understand them, answer questions about why they are happening and put measures in place that could help to reverse or mitigate them or encourage adaption to them.

Monitoring oceanographic conditions feeds directly into the uninterrupted five-year coral and reef fish monitoring programme run by the SOSF-DRC. In the coral aspect of the programme, the most detailed such programme in the Seychelles, the data collected include benthic cover and composition, growth rate and recruitment of corals and both broad- and fine-scale bleaching surveys. These surveys were particularly relevant during the bleaching event in mid-2016, as without prior monitoring of composition, recruitment and growth prior to the bleaching, there would be little to compare for recovery. Without baseline data such as these, it is difficult to pinpoint what constitutes a healthy reef. In the second part of the monitoring programme, data from reef fish surveys have shown abundant and diverse fish populations that have the potential to act as replenishing stock for the wider Seychelles.

A healthy coral reef system with abundant reef fishes provides support for larger top predators such as giant trevally Caranx ignobilis. Although this species is commercially and recreationally important throughout the Indian Ocean, virtually nothing is known about its life history. In 2016 the SOSF-DRC set out to use behavioural ecology and genetic analysis to investigate the population connectivity of this large species. For the Seychelles, a better understanding of the giant trevally could lead to improved management of the species and the prioritisation of exploiting it sustainably, which would benefit both the tourism economy and local food security.

Finally, another ocean giant, the reef manta Manta alfredi, is a popular resident in the waters surrounding St Joseph and D’Arros and it too has an established research project associated with it. With a local population exceeding 120 identified individuals, the mantas studied by the SOSF-DRC make up the largest and densest aggregation known in the Seychelles. Because the reef manta faces population declines throughout its range, understanding its ecology and movements is crucial to its survival as a species and its participation in the tourism industry. The conservation needs of the reef manta in the wider Seychelles are generally not known, but the species’ global ecotourism value of roughly $50-million makes finding out how best to protect it worthwhile in terms of both conservation and the economy.

Manta rays bask in the channel between D'Arros and St Joseph. These waters are home to a large population of resident individuals. The DRC is investigating the ecology and movement of the rays using acoustic transmitters. Photo by Thomas Peschak

Photo by Thomas Peschak

Just getting started

Ultimately, the SOSF-DRC has a strong history of supporting research to enhance and promote the conservation of important Seychellois ecosystems, species and heritage. Yet these projects are only the beginning; the centre has merely scratched the surface of the potential for St Joseph Atoll and D’Arros Island to unlock the natural secrets of the Seychelles.

The SOSF-DRC is ambitious when it comes to delving deeper into the ecosystems of D’Arros and St Joseph. In addition, its staff welcome the opportunity to work more closely with institutions such as the University of Seychelles to involve a growing number of interested Seychellois in this process. St Joseph Atoll and D’Arros Island are a national treasure, providing an almost pristine marine environment that is prime for both research and discovery.

Recognised globally as a UNESCO World Heritage Site, Aldabra is a shining example of the Seychellois people’s commitment to their natural heritage. By continuing to study and protect the unique elements of the ‘Aldabra of the Amirantes’ – St Joseph Atoll and neighbouring D’Arros Island – the Seychelles sends the message that it cares about future generations. The SOSF-DRC takes pride in joining in the commitment to and care of this special area.

Photo by Thomas Peschak

Project

SOSF D’Arros Research Centre

A biological field station based on D’Arros Island in the Amirantes Group, Seychelles, the SOSF D’Arros Research Centre (SOSF–DRC) conducts research on the pristine D’Arros Island and St Joseph Atoll and the waters around them. In recognition of the islands’ outstanding natural values, the research centre was established in 2004 and tasked with becoming a regional centre of excellence for marine and tropical island conservation. Initially, collaborations were established with local and international institutions and baseline ecological surveys were conducted in the various habitats. Over the ensuing years an increasing number of research projects and monitoring programmes were implemented in response to questions raised by the baseline surveys and by visiting scientists. More recently, the centre expanded its activities to include ecosystem restoration and environmental education.

Today the SOSF–DRC boasts the longest-running nesting turtle monitoring programme in the Amirantes and the most detailed and technically advanced coral reef monitoring programme in the Seychelles, making use of techniques such as stereo-video photogrammetry, photoquadrats, remote underwater video systems (BRUVs) and visual census. The research centre also maintains the largest acoustic receiver array in the Seychelles, which monitors the local movements of sharks, manta rays, stingrays, turtles and fish. Since its inception in 2004, the centre has initiated no fewer than 36 research projects in collaboration with more than 26 conservation institutions. The projects have resulted in 10 peer-reviewed scientific papers, one PhD and one MSc dissertation, five conference presentations and 27 scientific reports.